METHOD:

For the Seasoning for the Roll:
Combine the thick soy sauce, sugar, garlic, spring onions, sesame oil, and pepper in a medium bowl. Reserve.

For the Eggplant-Cucumber Roll:
Grill the eggplants, then dip them in ice water to peel them. Slice the cucumber into 4-centimeter strips. Sprinkle some salt on the cucumbers, press the water out. Bring a medium pot of water to a boil. Meanwhile, heat a wok over medium-high heat, then stir fry the blotted cucumbers. Blanch the bean sprouts in the boiling water, then season them with some salt, pepper, sesame oil, and some of the seasoning for the roll. Stir fry the Shiitake and pine mushrooms and season them with salt, pepper, and seasoning for the roll. Roll the cucumber and bean sprouts inside the eggplant. Slice the roll into sushi-size pieces.

For the Vinegar Soy Sauce:
Combine the vinegar, sugar, soy sauce, garlic, and sesame oil, and whisk them together.

To Assemble and Serve:
Plate the eggplant roll slices and pour the vinegar soy sauce into a dipping sauce dish. Put the dipping sauce dish next to the eggplant slices and serve.